1. Field of the Invention
The present invention relates generally to a modem, and more particularly, to a modem and a driving method thereof that estimates and compensates for a time offset due to time drift.
2. Description of the Related Art
In a wireless communication system, a clock source used in a transceiver (for example, a base transceiver station) and a clock source used in a receiver (for example, a terminal) may be different from each other. Thus, time drift between the transceiver and the receiver can occur due to a drift of each clock. If the time drift is not compensated for, receiving performance can be degraded. Accordingly, the receiver estimates time drift and compensates for the time drift.
A Code Division Multiple Access (CDMA) system can track time drifts using various methods. In the case of a rake receiver, time drifts are tracked in fingers using an Early-Late tracking loop method, a Tau-Dither tracking loop method, or modification methods thereof.
A receiver supporting a High-Speed Downlink Packet Access (HSDPA) protocol uses a chip-level channel equalization receiving method, instead of a rake receiver, to obtain improved performance, and to this end, channel estimation is performed in units of chips or in units of sub-chips.